Orang-utans normally steer clear of water. In the wild they rarely go near rivers and lakes, to avoid the crocodiles and snakes that lurk there. So it came as a surprise to conservationists when a group of orphaned orang-utans that had been relocated to Kaja Island in Borneo started getting wet for all sorts of reasons: one pair was even seen having sex in water. "My guess is that the male chose the location because there was less chance of him being interrupted by other, more dominant males," says Anne Russon of York University in Toronto, Canada.

"Orang-utans are famous for their fear of water," says Russon. "They have high body densities and can't help but sink." They're such lousy swimmers that some zoos have stopped surrounding enclosures with moats – too many orang-utans have drowned.

"One day we saw an adolescent orang-utan called Sif wade into deep water, hunker down and then lunge forward making simple paddling movements with her arms and legs," says Russon. "It was kind of like a bad dog paddle." Sif didn't get all that far – about a metre.